The purpose of this longitudinal research is to develop an assessment of 36- to 38-month-old children's knowledge of fundamental geometric spatial and shape concepts in order to predict to standardized and normed mathematical and spatial assessments at the age of 50 to 52 months, as children are on the verge of entering school. This study fills significant gaps in our understanding of a) the relation of early geometric competence to math readiness at school entry;b) the process by which children gain sensitivity to geometric forms and their properties;and c) the contribution of socioeconomic status to the development of foundational STEM abilities. The proposed research represents an original approach to characterizing the relation of geometric-spatial knowledge to mathematical ability in preschool children and is a critical prerequisite to the creation of curricular interventions on geometric knowledge. This study is impelled by the fact that both the Head Start Preschool Outcomes Framework and the National Council of Teachers of Mathematics, Curriculum Focal Points for Prekindergarten identify specific competencies needed for success in mathematics: "the ability to recognize, compare, and name common shapes...put together and take apart shapes," and "build pictures and designs by combining two- and three-dimensional shapes." Thus, our research directly addresses the development of those skills broadly considered to be crucial to starting a child on a successful trajectory of STEM learning. The first study, conducted when children are between 36 and 38 months, asks what children know about geometric forms. This measure will explore preschoolers'knowledge of geometric shapes and their names across diverse visual representations. Coupled with eye gaze-tracking technology we will be able to access both the product and process of their cognition. Central to this research is the development of a novel battery of geometric-spatial tasks designed to assess the ability of children to manipulate geometric forms in space. These tasks access children's geometric skills earlier than has been commonly evaluated. Additionally, vocabulary and number sense will be evaluated to provide IQ and mathematical knowledge controls. These children will then be revisited 14 months later when they are between the ages of 50 to 52 months. In this follow-up session, the children will be given a suite of validation assessments spanning mathematical ability, general intelligence, and visual-spatial ability. Performance at both points will be regressed to evaluate the ability of the novel geometric-spatial battery to predict mathematical ability. The substantial importance of this study is three-fold. First, it establishes the contribution of early geometric-spatial abilities to mathematical abilities prior to school entry. Second, these findings will provide evidence-based support for the development of preschool curricula supporting the STEM disciplines. Finally, the work contributes to the body of research on gender and socioeconomic factors in geometric, spatial, and mathematical knowledge and ability. Public Health Relevance: Little is known about how young children's knowledge of geometric concepts relates to their mathematical abilities. This study follows a group of preschoolers over the course of 14 months and assesses the development their geometric and mathematical ability using a suite of innovative new tasks involving manipulating two- and three-dimensional shapes. The results of this study set the foundation for the creation of preschool curricula that can enhance young children's geometric-spatial skills prior to kindergarten thus starting them on a good foot forward in science, technology, engineering, or math.